The present invention relates generally to gas turbine engines, and more particularly, to a system for supplying buffer air and ventilation air to the bearing compartments and shaft(s) in gas turbine engines.
In typical multi-shaft bypass jet turbine engines, one shaft supports the rotors of a low pressure compressor and a low pressure turbine and another shaft supports the rotors of a high pressure compressor and a high pressure turbine. Generally, each of the shafts is supported by bearings, and each bearing is lubricated by a forced lubrication system which circulates lubricating oil fed by a pump.
In the forced lubricating system, high pressure air is drawn from the high pressure compressor and is conducted to the exterior of the oil seals of the bearing compartments to keep the interior of the bearing compartments at a lower pressure than its immediate surroundings. This pressure differential prevents the lubricating oil from leaking out of the bearing compartments. In particular, high pressure buffer air drawn from the high pressure compressor is utilized because at least one of the bearing compartments is located in a high pressure environment where buffer air from the low pressure compressor would not provide adequate compartment pressurization at low power engine operating conditions. Unfortunately, buffer air drawn from the high pressure compressor is excessively hot and requires cooling at higher power engine operating conditions. Therefore, a dedicated cooler is required to lower the temperature of the buffer air. This cooler adds additional weight to the engine and can be difficult to package especially in smaller engine models.